Fischer-Tropsch (FT) synthesis can be utilized to convert syngas into clean sources of energy such as diesel and naphtha.1,2 To date only iron and cobalt catalysts have proven economically feasible on an industrial scale.2 The high water-gas-shift (WGS) reaction rate of iron makes it a useful catalyst for converting hydrogen-lean syngas derived from coal and biomass gasification processes.3 Improvements in catalyst selectivity, activity and stability are needed so as to improve FT process economy.3,4 
The addition of one or more promoters can have an influence on the selectivity and/or activity of FT catalysts. For example, the product selectivity of an iron catalyst can be controlled by promoting it with one or more alkali metals. Potassium is a chemical promoter that has been reported to increase wax and alkene yields while decreasing the production of undesirable methane in FT catalysts.5 Potassium promotion has also been reported to boost FTS and WGS activities of such catalysts. As CO tends to accept electrons from iron during the surface reactions of FTS, it has been postulated that potassium facilitates CO chemisorption due to its strong basicity because it can donate electrons to iron.6 Copper has been added to precipitated iron catalysts to facilitate the reduction of iron oxide to metallic iron during hydrogen activation. Addition of the copper has been said to minimize the sintering of iron catalysts when activating with hydrogen by lowering the reduction temperature.5 
It has been reported that the FT catalyst activity and selectivity can also be influenced by the nature and structure of the support, the nature of the active metal, metal dispersion, metal loading and the catalyst preparation method.7,8 For example, the support may have significant effects on the catalyst activity and selectivity due to metal-support interactions, porosity and mass transfer limitations. Most studies on FT catalysts have been carried out with the metal supported on silica, alumina or titania. For example, Qin et al. have reported the effects of Mo and Cu promoters on the properties of SiO2-supported FeK catalysts and their Fischer-Tropsch synthesis (FTS) performance.9 
Other supports such as carbon in the form of activated carbon (AC) and carbon nanotubes (CNTs) have also been investigated in FT reactions.10,11,12,13,14,15,16,17,18,19,20,21,22,23,24 For example, it has been reported that an iron catalyst supported on AC showed a higher throughput per unit volume as a consequence of higher dispersions and/or metal-support interactions, and higher olefin selectivity than unsupported iron catalysts.25,26 
Ma et al. have reported iron catalysts with Mo—Cu—K additives for use in Fischer-Tropsch synthesis (FTS) supported on a number of activated carbons.27,28 A study of the physico-chemical properties of activated carbon-supported Mo promoted Fe—Cu—K catalysts as a function of Mo loading (0-12%) has been reported by Ma et al.29 
As mentioned above, CNTs with unique properties such as meso and macro pore structure, uniform and straight pores, inert surface properties, resistance to acidic and basic environments, and ease of recovery of metals from spent catalysts have been reported as a support for catalytic reactions. There have been a few studies on the application of CNTs as a support for Co and/or Fe catalysts for use in FTS.14,15,18,19,20,21 
Tavasoli et al. discloses a catalyst prepared by incorporating cobalt, ruthenium, and optionally an alkali metal, for example, K onto a CNT support for the conversion of synthesis gases into a mixture of essentially linear and saturated hydrocarbons.15 The use in FTS of mono- and bimetallic Co and Fe catalysts supported on CNTs has also been reported.30 
Bahome et al. reported iron-based catalysts supported on CNTs for use in the FT reaction promoted with potassium and/or copper.21 
Malek Abbaslou et al. have reported the effect of pre-treatment with room temperature (25° C.) or refluxing (110° C.) nitric acid on CNT-supported catalysts with approximately 10 wt % iron content.31 Malek Abbaslou et al. have also reported catalysts with approximately 12 wt % iron supported on CNTs wherein the position of the catalytic sites was varied to be primarily on the inner or primarily on the outer surface of the nanotubes.32 Malek Abbaslou et al. have further reported catalysts with approximately 20 wt % iron supported on CNTs with narrow (average size 12 nm) and wide (average size 63 nm) pores.33 